This invention relates to a liquid coating supply system for a coater which applies the liquid coating material to the blanket cylinder of a web offset printing press for coating the printed paper as it is moving through the press. The coating material may be an aqueous coating which when dry renders the printed paper resistant to moisture and oils and prevents smearing. The coated paper may have a glossy or matte finish.
It has become common practice to utilize a coater for applying a liquid coating material to the blanket of a web offset printing press so that the printed sheet which is moving through the press can be coated. These coaters generally utilize a tray for holding the liquid coating material and a feed roller rotating in the liquid coating material in the tray. A coater roller is in rotating engagement with the feed roller and also in rotating engagement with the blanket roller of the printing press. The coating material is picked up from the tray by the feed roller, transfered to the coater roller, and retransfered to the blanket by the coater roller.
In this system it is important to maintain a pool of coating material in the tray and also to constantly recirculate the coating material so that the material is constantly entering the tray and constantly leaving the tray in the recirculation system.
Previous systems required continuous attention by the operator and adjustments to make sure that the system did not starve or overflow. Since the coating material is generally a sticky, varnish-like material considerable difficulty would result if the tray were to overflow into the works of the printing press. If the system is starved, i.e., has an undersupply of coating material, the tray will run dry and the coating material will not be transferred to the blanket and the printed sheet will not be properly coated.
It is necessary that the amount of liquid coating delivered to the tray be at least equal to that taken up by the feed roller and deposited by the coater roller on the blanket otherwise the tray will run dry. However, if the amount of coating material being delivered to the tray is too high, the tray will overflow with disastrous consequences to the press.
It is an object of this invention to provide a liquid coating supply system which will permit sufficient amount of liquid coating material to be delivered to the tray, but prevent the delivery of more material to the tray than can be taken away from the tray by the recirculation system.
The recirculation system disclosed herein prevents any possibility of the material being delivered to the tray in such quantities that the tray will overflow.
The liquid coating supply system constructed in accordance with this invention comprises a vessel for containing a supply of liquid coating material, a holding tray for holding a portion of the liquid coating material for pick up by a feed roller, a first liquid transfer means for transfering the liquid coating material from said supply vessel to said holding tray, and second liquid transfer means for transfering the liquid coating material from the holding tray to the supply vessel.
The first liquid transfer means includes an adjustable flow valve for regulating the liquid flow from the first liquid transfer means and a supply pump means between the supply vessel and the adjustable flow valve for withdrawing coating material from the supply vessel and for forcing the material through the valve under a pressure which is dependent upon the adjustment of the valve. This transfer means further includes a pressure responsive means between the pump and the adjustable valve for conducting the liquid flowing from the pump back to the supply vessel when the pressure between the pump and the adjustable valve exceeds a predetermined value.
The second liquid transfer means preferably also includes a supply pump means between the holding tray and the supply vessel for withdrawing the liquid coating material from the holding tray and forcibly pumping it into the supply vessel at a rate of flow which is at least equal to the rate of flow from the first liquid transfer means to the holding tray. The intake of this second transfer means is located above the bottom of the tray at the desired level at which the liquid is to be maintained in the tray. The discharge pump will withdraw the liquid coating material from the holding tray after the material in the tray rises to the level of the intake of the second transfer means.
It is preferred that the operating elements of the supply pump means and the discharge pump means be interconnected so that the operating elements will operate in unison with the strokes of the operating elements being substantially the same. In view of the adjustable valve at the discharge end of the first liquid transfer means and the pressure responsive means in that first liquid transfer means which transfers a portion of the fluid back to the supply vessel, the amount of fluid arriving at the holding tray from the first liquid transfer means will be less than the capacity of the second liquid transfer means to withdraw the liquid from the holding tray. As a result, the holding tray will never accumulate liquid coating material over a predetermined amount, i.e. over the level of the intake of the second transfer means, and it will never overflow.